Before spending the bucks on a digital camera, work on photographic technique. Equipment doesn't make the picture --the photographer does. You need to know the fundamentals of the photographic process no matter what type of gear you use. There are a lot of good books that will explain things like exposure. If outdoor photography is your thing, look at John Shaw's books -- "Nature Photography Field Guide" and "Landscape Photography". This is A LOT less expensive that a D70 and will get you A LOT more good pictures.

Regards
Dennis